Thanks Lorenz
I figured out the union thing too so I ended up using the below SPARQL
instead and it seems to work fine but would love to know what is the
equivalent using Jena API
"SELECT DISTINCT ?s WHERE { " +
"?s a owl:Class . " +
"FILTER (!isBlank(?s)) " +
"FILTER (?s != owl:Thing && ?s != owl:Nothing) . " +
"OPTIONAL { " +
" ?s rdfs:subClassOf ?super . " +
" FILTER (?super != rdfs:Resource && ?super != owl:Thing
&& ?s != ?super) " +
" } . " +
"FILTER (!bound(?super))" +
"}");
Regards
On Thu, Sep 5, 2019 at 8:00 PM Lorenz Buehmann <
buehm...@informatik.uni-leipzig.de> wrote:
> schema.org contains a bunch of anonymous classes like the union of other
> classes which are used as domain or range of a property, that's why you
> get null values because they do not have a URI. If you'd just call
>
> |System.out.println(clazz);|
>
>
> you'd see the blank node Ids.
>
>
> Among all those blank nodes, there is indeed the one top level class
> http://schema.org/Thing .
>
>
> I thought just adding a filter on the iterator is enough, i.e.
>
> |topClazzez = topClazzez.filterDrop(OntResource::isAnon);|
>
>
> but while it doesn't return the blank nodes anymore, it leads to an
> exception:
>
>
> |Exception in thread "main"
> org.apache.jena.ontology.ConversionException: Cannot convert node
> http://www.w3.org/2000/01/rdf-schema#Class to OntClass: it does not have
> rdf:type owl:Class or equivalent||
> || at
> org.apache.jena.ontology.impl.OntClassImpl$1.wrap(OntClassImpl.java:82)||
> || at org.apache.jena.enhanced.EnhNode.convertTo(EnhNode.java:152)||
> || at org.apache.jena.enhanced.EnhNode.convertTo(EnhNode.java:31)||
> || at
> org.apache.jena.enhanced.Polymorphic.asInternal(Polymorphic.java:62)||
> || at org.apache.jena.enhanced.EnhNode.as(EnhNode.java:107)||
> || at
>
> org.apache.jena.ontology.impl.OntResourceImpl.lambda$listDirectPropertyValues$8(OntResourceImpl.java:1536)||
> || at
> org.apache.jena.util.iterator.Map1Iterator.next(Map1Iterator.java:46)||
> || at
>
> org.apache.jena.ontology.impl.OntResourceImpl.computeDirectValues(OntResourceImpl.java:1580)||
> || at
>
> org.apache.jena.ontology.impl.OntResourceImpl.listDirectPropertyValues(OntResourceImpl.java:1553)||
> || at
>
> org.apache.jena.ontology.impl.OntClassImpl.listSuperClasses(OntClassImpl.java:180)||
> || at
>
> org.apache.jena.ontology.impl.OntClassImpl.isHierarchyRoot(OntClassImpl.java:739)||
> || at
>
> org.apache.jena.util.iterator.FilterIterator.hasNext(FilterIterator.java:56)||
> || at
>
> org.apache.jena.util.iterator.WrappedIterator.hasNext(WrappedIterator.java:90)||
> || at
>
> org.apache.jena.util.iterator.FilterIterator.hasNext(FilterIterator.java:55)||
> || at com.company.Main.main(Main.java:25)|
>
>
>
> On 05.09.19 03:11, Alex To wrote:
> > Hi I am trying to load schema.org ontology and get all top classes
> > using ontModel.listHierarchyRootClasses() but can't get the expected
> > results with different OntModelSpec.
> >
> > If I use OWL_MEM, it lists 2500+ records with all the records have "null"
> > URI.
> > If I use OWL_DL_MEM, it lists 0 records
> >
> > The code is very simple as follows
> >
> > Model model = ModelFactory.createDefaultModel();
> > model.read("https://schema.org/docs/schemaorg.owl";);
> > OntModel ontModel =
> > ModelFactory.createOntologyModel(OntModelSpec.OWL_MEM, model);
> > ExtendedIterator<OntClass> topClazzez =
> ontModel.listHierarchyRootClasses();
> > while (topClazzez.hasNext()) {
> > OntClass clazz = topClazzez.next();
> > System.out.println(clazz.getURI());
> > }
> >
> > A minimal Maven project ready to run to demonstrate my problem is here
> > https://github.com/AlexTo/jena-lab (have a look at the Main.java)
> >
> > Thanks a lot
>
--
